Center for Functional Nanomaterials Seminar

I will describe a materials and electrical study of transition-metal oxide based "memristive" elements. These nano-patterned crossbar structures exhibit a dramatic electrically-driven resistance change and have applications in computation, sensing, high density memory, and synaptic (neural) computing. Although heavily characterized electrically, an understanding of the physical changes induced during the resistance switching has been limited due to the challenges of observing very subtle material changes occurring in a nanoscale volume between metal contacts. I will describe a set of experiments measuring the electronic, chemical, and structural properties within functioning devices with nanoscale spatial resolution using x-ray and electron based spectroscopy and microscopy techniques. These experiments have shed light on the physical mechanism underlying the electrical behavior and revealed the occurrence of interesting phase changes and shown the key role played by oxygen vacancies. Unexpectedly, the vacancies condense into a long-range ordered phase which becomes the focal point for resistance switching. Significant heating is also observed to occur in nanoscale volumes during electrical operation, which may further accelerate key electrochemical and ionic processes involved. I will address the generality of the observed switching mechanism to other oxide systems and how this material knowledge has yielded improvements in the devices. Finally, I will show single-shot, sub-nanosecond electrical measurements which explore the high speed dynamics and probe the characteristic time-scales of the material changes.